Certain highly ring-substituted liquid aromatic diamines such as diethyltoluenediamine are effective curatives (curing agents) for polyurethanes and epoxy resins. Other uses include use as extenders for polyurethane elastomers, particularly in RIM applications, use as monomers, and use as antioxidants for elastomers, lubricants, and industrial oils. Unfortunately such highly substituted liquid aromatic diamines are highly sensitive to development of coloration, so much so that even when such materials are produced under an inert atmosphere such as nitrogen, color can develop when transferring the diamine product into containers. Prevention of such color development in commercial plant facilities cannot be accomplished economically.
During storage after exposure to air the coloration of such highly ring-substituted liquid aromatic diamines typically becomes progressively darker, even to the point at which the material appears almost like black ink to the naked eye. To ameliorate this problem it has been recommended that the purchaser of such a product maintain the product under a nitrogen atmosphere during storage to at least keep the existing yellow or amber coloration from reaching the black stage.
Since coloration in the product can detract from its sales appeal, a need has existed for an effective, economical way of decolorizing such aromatic diamine.
In Japan Kokai No. SHO 59-42346 published on Mar. 8, 1984 it is shown that m-phenylenediamine which initially had a standard color rating of 200 remained at the same color level for 3 days after addition thereto of 0.5% of diethylhydroxylamine, and thereafter suffered an increase in coloration to a rating of 300 at 7 days after the addition.